The present invention relates to laminated wiring cables, and pertains particularly to a method and apparatus for lamination of flex cable circuits.
Multi-layer printed wiring cables are manufactured by a laminating process wherein multiple printed circuits, each of which is formed by a flexible carrier provided with a conductor pattern formed on at least one side thereof, are laminated together. The layers are usually secured together by an adhesive which is cured by process of applying temperature and pressure. During this process of lamination, air within the space between the platens between which the layers are pressed is frequently evacuated.
While the prior art techniques have been found to be suitable in situations where highly fluid adhesives are used, such techniques are unsuitable where very low flow, or no flow, adhesives are used. These prior art techniques have resulted in inadequate evacuation of the air from the chamber with the result that air is trapped between the laminations.
It has also been found that prior art fixtures have a number of drawbacks. Such drawbacks include the complicated structures which greatly increase the production time in the processing. The prior art fixture structures for such techniques typically employ a barrel structure having a side wall with end plates sealed to or sealably engaging the side walls and the vacuum connection to the interior of the barrel being through the side wall. This presents difficulties in sealing the structure for drawing an adequate vacuum. Other forms of vacuum laminating structures of fixtures involving the use of vacuum also have sealing difficulties which complicates the manufacturing process.
The prior art approach to wiring cable laminations is exemplified, for example, in U.S. Pat. No. 3,960,635, issued June 1, 1976 to Leroy et al. This patent is directed to a method of fabrication of printed circuits and schematically illustrates a fixture for carrying out the process. This patent discloses the typical barrel fixture technique. The patent also fails to appreciate or recognize the necessity for complete evacuation of the fixture prior to application of laminating pressure.
Other patents of somewhat general interest includes the Willett patent, U.S. Pat. No. 3,444,275, issued May 13, 1969, and directed to a method of molding utilizing dielectric heating. The fixture utilizes separate walled chambers defined by annular walls 24 which surround plates 22 and 23 and through which the vacuum conduits extend.
It is desirable that improved method and apparatus be available for the formation of laminated multi-layer printed wiring cables.